A note on photocurrents in extrinsic semiconductors

The absorption of light generates excess carriers (electrons and holes) in a uniformly doped semiconductor and sets up diffusion currents. Owing to the difference of the diffusion constants for electrons and holes, the diffusion currents produce a small electric field in a zero current configuration. This is well known. It is not realized generally that fairly large electrical currents of ten's of mA can be generated under short circuit conditions. Theoretical treatments of these effects in the literature are logically flawed. In this paper the situation will be remedied.